Try...
Code:
.simple-search-box {
border: 2px solid #000 !important;
}
.simple-search-box > input,
.simple-search-box > input::-webkit-input-placeholder,
.simple-search-box > input::-moz-placeholder,
.simple-search-box > input:-ms-input-placeholder,
.simple-search-box > input:-moz-placeholder,
.simple-search-box > button[type="submit"] {
color: #000 !important;
opacity: 1 !important;
}